It is the best of times, it is the worst of times. Spain are European and world champions, the most successful national team in history. They completed a unique three-tournament run with a 4-0 demolition of Italy, the biggest winning margin in a final.

Meanwhile, Barcelona and Real Madrid are arguably the most powerful clubs the game has seen. The favourites for this year's Ballon d'Or will be theirs. Again. Since 2005, only one winner of the award for the world's best player didn't play for Real or Barcelona and Kaká and Cristiano Ronaldo ended up arriving at the Bernabéu anyway.

For the past two years Real and Barcelona have boasted all six of the men on the podium, Ronaldo breaking up Barça's domination. With every passing week, Real and Barcelona, Ronaldo and Leo Messi, break records that seemed to belong to another era. Ronaldo broke a 38-goal record that had stood for 20 years. The very next season, Messi reached 50. Barcelona reached 99 points, two years later Madrid hit 100. Impossible figures suddenly look easy.

One of the reasons that they rack up such astonishing totals is that, in a battle where draws are the new defeats, they have to. The pressure is suffocating; these two teams drive each other, all too aware that the smallest slip could be decisive. The other, related reason is that they can.

The Spanish league is not easy. Barcelona and Real have been European semi-finalists for the past two years and they are favourites for the final this year, too. These are genuinely brilliant teams with genuinely brilliant players, some of the best in history; they are teams who would surely win the English title. Every time the doubters say of Messi: "I'd like to see him score those goals in a decent league," the obvious retort is: "How about the Champions League? That's quite a good league and he has been top scorer there for four seasons in a row." When they point the finger at Ronaldo, it is simple to recall his 42-goal season in Manchester.

Last season's Europa League final featured two Spanish teams: Athletic Bilbao and Atlético Madrid. Atlético won their second title in three years – Spanish clubs have won five of the last nine. If the Uefa Cup is the tournament that measures the depth of a league's talent, then Spain's league is amongst the strongest. If La Liga is a two-horse race, which it is, it is not because the rest are a bunch of donkeys. At least not yet. José Mourinho insisted that any team in the world that joined La Liga would come third, behind the big two.

He is right in the short term. But the trend is not just to the defeat of the other clubs but to their destruction. To the destruction of the league. And the league itself is complicit in its demise. This week, 13 clubs joined up to try to force the Liga de Fútbol Profesional to address the issue. They wanted a change in the TV model, a more equal distribution of the money and the kick-off times. The opening two weeks of the season include nine different slots, and 11pm kick-offs on Sunday night. More immediately, the clubs wanted the LFP to defend them in their battle with the TV company that, they allege, has not paid them. There was even talk of a strike, of the season not starting.

They failed in their bid. The LFP is run by the president who drove Real Sociedad into economic crisis and the man who boasts of handling the TV rights of 30 clubs across the two divisions and somehow does so without anyone questioning how it has come to this and in whose interests he does so. The Atlético president Enrique Cerezo noted that the league is supposed to be defending the rights of all the clubs, but that does not appear to interest them. "The rest of Europe laughs at us," said Espanyol's CEO Joan Collet. The good news is that the league finally got the go-ahead – five days before it was due to go ahead.

It is well-documented that TV deals are signed individually in Spain. Real and Barcelona make three times more than Valencia and Atlético, the next highest earners. That is not the only source of their income, but it is the most significant. €120m against €42m a season may not sound like much but season after season after season, the impact is gigantic.

This is an economic and social reality: almost two-thirds of the country claim to be Real or Barcelona fans first, while most of the remaining third are also Real or Barcelona fans second. Millions watch them, while one Spanish federation official privately reveals that the number of pay-per-view hits on one game not involving Real or Barcelona a couple of seasons ago was 47. Yes, 47. And that's the home market; the international market is almost entirely captured by the two clubs.

There is a difference between the same two (or three, or four) teams winning the league and the same two teams winning virtually every game. It is not normal for four- or five-goal victories to be more common than one- or two-goal victories, but that is what is happening. Last season, Valencia finished third. They were 39 points behind the champions. The season before the gap was 25 points and the season before that 28. Before that, Sevilla were third. They were 27 points behind.

That is a reality. It is a footballing and a financial fact. It is also self-perpetuating, it creates an upward spiral for the big two and a downward spiral for the rest. Jordi Alba has signed for Barcelona from Valencia, Luka Modric of Spurs will probably sign for Real. Over the past three seasons, a case can be made to say that the Spanish league has taken the best player from the Premier League (Ronaldo, Fábregas), Serie A (Kaká, Ibrahimovic) and the Bundesliga (Sahin). But that case depends on you treating the Spanish league, Barça and Real as synonymous, acting like they and they alone are the Spanish league. Which is exactly what they do. It is what they do, the TV operators do and the media do. It is what many fans do, too.

Spain play in Puerto Rico on Wednesday evening. Another transatlantic friendly no one cares about and four days before the season starts. The only debate is whether Real and Barcelona's players will play the same number of minutes. No one cares about the rest.

The big two keep improving; for the rest, standing still is as much as they can aspire to. This summer Valencia's most expensive player cost €3.7m. Sevilla's cost €3.5m. They are the highest-priced signings outside the big two. Most cannot even do that.

This summer, Real and Barcelona have spent more money on players for their B teams than half of the league has on players for their first teams. Instead players depart. Even on the Costa del Sol. The one team that could in theory have challenged the big two was Málaga. But a year after spending almost €60m on players, their Qatari owner, Sheikh Al-Thani, has pulled the plug. Santi Cazorla went, Salomon Rondon, too, and there may yet be more leaving.

The bottom line is that people want to watch the best players and, in that sense, Spain's top league remains the best in the world. If you want to see Messi and Ronaldo play, you have to watch La Liga. But because of their dominance, because of Real and Barcelona's power, other good players are no longer on display.

The best of times, the worst of times: best and worst are not mutually exclusive concepts, in fact, they are related. The lack of money in La Liga, beyond the big two, means greater opportunity for Spanish players. But those players tend to end up dragged into the orbit of the big two. Valencia had four World Cup winners; within a year they had none, all of them having departed. Another reached the Spain squad for Euro 2012 but by the time the final arrived Alba had joined Barcelona.

Of the starting XI, only David Silva was not a Real or Barcelona player, and he had left the league. It is a familiar career path. Even Real and Barcelona cannot house every good player. The best players in Spain not at the big two now have one of two choices if they want to earn big salaries and compete to win things: go to one of the big two or leave Spain altogether.

Outside the big two, who have been the best players in Spain over the last five years or so? The sudden stars to emerge? The men who got you most excited? The dominant players? Sergio Agüero? Dani Alves? David Villa? Diego Forlan? Giuseppe Rossi? Fernando Llorente? Juan Mata? Cazorla? Sergio Canales? Radamel Falcao? Of course there are exceptions but the pattern is obvious. Where are they now? At one of the big two or abroad. Why hang around? A drift towards Madrid and Barcelona is not new; but now it is not so much a drift as a sprint. The process has been accelerated.

Of that list above, Rossi is still at Villarreal because they chose to sell Cazorla instead, and, despite suffering two knee ligament injuries in a year, will surely be on his way soon. Falcao is still at Atlético, but they only own half of his rights. And this week it was announced that Llorente wants to leave Athletic. No one even contemplates the possibility that it will be to join one of Spain's "other" clubs.

Even Michu went this summer, leaving Rayo for Swansea City. And this week, Arouna Koné departed Levante. That means, assuming Llorente goes, apart from Real and Barcelona, all of the teams that have qualified for European football have lost their best player, except Atlético. And if they kept Falcao, they did lose Diego. No wonder the gap gets bigger, no wonder the league gets reduced to two teams. The haemorrhage continues and it could prove fatal. The departure of Cazorla was bad news for Málaga and for the league, the confirmation of a trend. Worse, the evidence that the one club that could have bucked the trend cannot.

This season will again throw up great narrative and great characters. Wonderful players will emerge – keep an eye on Oliver Torres at Atlético – and there will be new heroes. There will be fascinating plots and there will be life beyond the big two. There always is, even if it goes ignored too often and by too many. The fear though is that it will have a familiar ending. When those players do emerge, they will watch Real and Barcelona disappear into the distance and they too will have to make a choice. Sign for them. Or leave Spain.